1. Field of the Invention
This invention relates in general to an apparatus used in the fabrication of semiconductor devices, and more specifically, to a reticle used in the manufacture of semiconductor devices employing photolithography.
2. Description of Related Art
The use of lithographic technology in transferring patterns from photomasks to semiconductor substrates in the fabrication of semiconductor devices, such as integrated circuits, has been highly developed and widely used. Reticles, or photomasks, are used with a variety of radiation sources, both visible and ultraviolet, as well as x-rays and electron beams.
A typical reticle comprises a transparent substrate, such as glass, quartz and the like, which is coated with a masking layer patterned to be complementary to the pattern desired to be transferred to a silicon wafer. Such masking layers are generally materials such as chromium, chrome oxide, iron oxide, nickel and the like. These materials are deposited on the substrate by conventional techniques known in the art.
In photolithography, transmission of light through the substrate of the reticle is about 96.0%. Thus, about 4% of the light is reflected at the interface of the substrate facing the silicon wafer and the air. Light passing through the substrate and hitting the masking layer is completely reflected at the substrate/mask interface. The 4% inherent reflectance of the reticle at the substrate/air interface increases the exposure time to pattern the silicon wafer leading to slower production and increased cost per wafer.
The glass substrate will typically become statically charged during handling. Even the smallest amount of static charge will attract dust and particles to the glass surface further degrading the circuit pattern projected on to the semiconductor substrate.
Static electricity due to the motion of objects or air around the reticles builds up on the reticles. Electrostatic discharge (ESD) results when the opposite charge between objects reaches a threshold, and the charge is passed between the objects. Depending on the degree of charge and an object's material sensitivity, the exchange of charge can cause damage to the object. In the case of very small mask photolithographic design structures, such as reticles, this damage can be severe enough to melt and/or blast the chrome structure. This causes mask damage including opens, re-deposited chrome, and severed geometries. The damage results in wafer scrap, rework, mask repair and rebuild, and considerable engineering and manufacturing time spent on in-line inspections and defect analysis.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a reticle having reduced inherent reflectance improving the transmission of light when transferring the pattern onto a semiconductor substrate.
It is another object of the present invention to provide a reticle having optimal transmission and reduced ESD.
A further object of the invention is to provide a method of fabricating a static resistant reticle having optimal transmission and reduced ESD.
It is yet another object of the present invention to provide a method of patterning a silicon wafer in a semiconductor device with enhanced transmission of light and reduced ESD providing enhanced clarity of the reticle pattern.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.